Lawn and garden tractors and other utility vehicles may include all-wheel steering mechanisms which serve to turn all four ground engaging wheels. This provides the capability of executing relatively tight, small radius turns. For example, a tight turning radius may be desirable when using a lawn tractor to mow close around obstacles such as trees, posts or similar obstructions.
All-wheel steering mechanisms typically include an arm that translates or shifts forward or backward as the steering shaft pivots in response to the steering wheel being turned. Examples of all-wheel steering systems are shown in U.S. Pat. Nos. 5,174,595, 6,131,689 and 6,684,974 assigned to Deere and Company of Moline, Ill. U.S. Pat. No. 5,174,595 entitled “Four Wheel Steering Mechanism” relates to a steering linkage extending along the left side of the vehicle, which includes front and rear rod members that pivot, and an intermediate rod member that shifts longitudinally, as well as slightly laterally and vertically. U.S. Pat. No. 6,131,689 entitled “All-Wheel-Steer Biasing Mechanism” relates to a steering linkage having a front link element and a rear link element, both of which shift fore or aft to turn the front and rear wheels, and a biasing mechanism for biasing the rear wheel steering linkage back to a position for straight forward travel. U.S. Pat. No. 6,684,974 entitled “Four-Wheel Steering System for Utility Vehicle” relates to a linkage assembly that transforms pivoting motion of the front steering arms to pivoting motion of the rear steering arms, and eliminates the need for a front center-pivot.
All wheel steering systems are relatively costly and complex to manufacture and assemble, and may require many more parts and components than two wheel steering systems. There is a need to reduce the cost, complexity and number of parts and components in an all wheel steering system.
All wheel steering systems also require considerable space under the vehicle frame for link elements that translate or shift forward or backward when executing a turn. For example, drag links and bell cranks in an all wheel steering system may transmit motion for turning the front and rear wheels, and consume space under the frame that may be desirable for other parts and/or functions. There is a need to reduce the space requirements for an all wheel steering system.
In the past, all wheel steering systems also may not offer an equal turning radius in both directions. For example, the arm and/or link rods may not swing forward as far as backward. There is a need for an all wheel steering system that provides a more equal turning radius in both directions.